Girls and Boys

There is some deep irony in the fact that I bristle when I'm sitting in a meeting with my (male) health insurance broker and he makes reference to a "girl" at the insurance carrier - and hell yeah I corrected him - because I work in an industry where grown professional dancers are routinely called girls and boys. Apollo? It's for three girls and a boy. Antique Epigraphs? Eight girls. And it's not just in the ballet world - someone sings "How many boys, how many girls?" in A Chorus Line.

It doesn't rankle me that the dancers are girls and boys, but it's reflexive for me to get on a high horse when someone calls a grown woman a girl. Why?